Volume 14, Issue 1 (July 1992)

Sludge Ash Pellets as Coarse Aggregates in Concrete

This work examines the potential of using sintered sludge ash pellets as a substitute for regular coarse aggregate in concrete. The mixing of concrete samples was done by replacing the coarse aggregate with sludge ash pellets in varying proportions following mixing procedures of ASTM Test Method of Making and Curing Concrete Test Specimens in the Laboratory (C 192-88). Specimens were prepared as 50 by 100-mm cylinders and tested for compressive strength for up to 28 days. The results indicate that the incorporation of pellets produced reasonably strong concrete—4900 to 5910 psi (33 to 42 MPa) after 28 days. No adverse effects on concrete strength were observed. Instead, the pellets, being round in shape, enhanced the workability of concrete and resulted in more compact concrete specimens. The net result of substituting the pellets for coarse aggregates is to yield a concrete of lower density since the pellets are formed from a material of lower specific gravity than conventional aggregates. The data show that concrete containing pellets is lighter than regular concrete and has a better strength-to-weight ratio. The peak benefits are a strength-to-weight ratio improvement of more than 15% over regular concrete observed in the specimen with 35% substitution of coarse aggregate by pellets.